Optical pickup device and optical drive device

Abstract

An optical pickup device includes a semiconductor laser that emits a laser beam, and an object lens that concentrates the laser beam emitted from the semiconductor laser on an optical disc. In this optical pickup device, an optical axis of the object lens is inclined with respect to an optical axis of the laser beam that is incident on the object lens so as to generate flares caused by coma aberration on an entrance side in a forward direction of pits of the optical disc.

The invention claimed is: 
     
       1. An optical pickup device comprising:
 a semiconductor laser that emits a laser beam; and 
 an object lens that concentrates the laser beam on an optical disc, 
 wherein an optical axis of the object lens is inclined with respect to an optical axis of the laser beam that is incident on the object lens so as to generate a flare caused by coma aberration on an entrance side in a forward direction of pits of the optical disc. 
 
     
     
       2. The optical pickup device according to  claim 1 , wherein an inclination angle of the optical axis of the object lens with respect to the optical axis of the laser beam that is incident on the object lens is between 0.02 deg and 0.38 deg inclusive. 
     
     
       3. The optical pickup device according to  claim 1 , further comprising a diffraction element provided on an optical path between the semiconductor laser and the object lens,
 wherein the diffraction element is provided with a first diffraction grating with duty of grating becoming smaller from a central portion toward an outer edge. 
 
     
     
       4. The optical pickup device according to  claim 3 , wherein
 the first diffraction grating is provided on a first principal plane of the diffraction element, and 
 a second diffraction grating for dividing the laser beam into at least three beams and causing the divided beams to be incident on the object lens is provided on a second principal plane of the diffraction element on an opposite side of the first principal plane. 
 
     
     
       5. The optical pickup device according to  claim 4 , wherein the diffraction element is disposed so as to cause the laser beam to be incident on the first principal plane. 
     
     
       6. An optical drive device comprising:
 the optical pickup device according to  claim 1 ; and 
 a signal processor that performs signal processing on an electric signal that is output from the optical pickup device.